1. Field of Invention
The present invention relates to a source driver and a data switching circuit thereof, and particularly to a source driver and a data switching circuit thereof suitable for dot-inversion driving mode.
2. Description of the Related Art
A source driver is an important module in a TFT LCD (thin film transistor liquid crystal display). The source driver is in charge of transferring digital data signals for displaying frames into analog signals, which are then output to every sub-pixel, or called a dot.
FIG. 1 is a schematic structural block diagram of a conventional source driver 100. A source driver 100 receives a data signal 110 and outputs the analog signal through N pieces output channels Y1˜YN. The source driver 100 includes a shift register 101, a line latch 102, a level shifter 103, a digital-to-analog converter (DAC) 104 and an output buffer 105. The regular source driver is a conventional technology, and structure or the function thereof should be well known by those skilled in the art. In brief, the shift register 101 is used for allocating the data signal 110 to the output channels Y1˜YN, the line latch 102 temporarily stores the data signal and the level shifter 103 amplifies the data signal. Further, the digital-to-analog converter (DAC) 104 transfers the data signal into an analog signal. Finally, the output buffer 105 outputs the analog signal.
In a TFT LCD, liquid crystal is used as the material for controlling display. To avoid liquid crystal polarization, an AC (alternating current) voltage is applied for driving the voltage, not DC (direct current). Therefore, there are various inversion driving modes, such as column-inversion mode, line-inversion mode and dot-inversion mode, and so on. FIG. 2 is a diagram showing the dot-inversion driving mode. Wherein, the sub-pixels driving polarities of a TFT LCD for a frame T and the next frame T+1 are shown, and + indicates a positive polarity driving mode, while − indicates a negative polarity driving mode. It can be seen from FIG. 2 that the so-called dot-inversion means any two adjacent pixels on a frame in either horizontal direction or vertical direction, have opposite driving polarity, respectively; further, on the next frame, all pixels alter the driving polarity thereof.
The dot-inversion driving mode has a lot of advantages. However, the biggest disadvantage of the dot-inversion driving mode is the large power consumption. FIG. 3 is a diagram showing signal waves of a conventional dot-inversion driving mode, wherein a source driver 301, through an output buffer 302 and data tines DL0˜DL3, outputs analog signals to sub-pixels SP0˜SP3 located on a same scan line SL in a pixel array 303. The panel of a modern large-screen TFT LCD is mostly designed to use a DC common voltage Vcom; thus, there are a positive-polarity voltage higher than the common voltage Vcom and a negative-polarity voltage lower than the common voltage Vcom. In FIG. 3 for example, the voltage polarity output from the data line DL0 and DL2 is, in sequence, positive, negative and positive; while the voltage polarity output from the data line DL1 and DL3 is, in sequence, negative, positive and negative. Every time when entering a next scan line or a next frame, the voltage polarity of the data lines DL0˜DL3 must be inverted. Therefore, the source driver 301 should provide an applied voltage Vswing of around two times as large as the common voltage Vcom. With a larger applied voltage Vswing, more power consumption is required. In addition, to meet the trend of larger screen, higher resolution and wide viewing technology, for example, in-plane switching (IPS) or multi-domain vertical alignment (MVA), a higher driving voltage is essentially needed, which complicates the above-described problem.